In ACS is there a GET or what would the path be to pull back say the transactional email event that was setup.
A get on the event that was create gives you history but how about the actual container(meaning email content) to parse variables in the email
You can get it using below request (access token to be passed for Authorization header in Postman).
Get template-id from the URL (Administrators > Marketing Plans > Transactional Messages > Transactional Messages > Select the template )
There is also an option (under Content Source) to get the template from AEM where you can parse and change i t programmatically as needed.